Suppose that fast forward playback or fast reverse playback of moving pictures in MPEG (Moving Picture Experts Group)2 format recorded on recording media, such as, for example, DVDs (Digital Versatile Discs) is performed. In the fast forward playback, the moving pictures are played back in a forward direction at a speed faster than a normal playback speed, whereas in the fast reverse playback, the moving pictures are played back in a reverse direction at a speed faster than the normal playback speed.
FIG. 1 shows an example of a structure of moving pictures in MPEG2 format recorded on a DVD or the like. A series of the moving pictures consists of a plurality of GOPs (Groups of Pictures). The elements of series of GOPs are referred to as GOP#1, GOP#2, GOP#3, . . . , GOP#(N−1), and GOP#N from the first GOP in a playback order. Thus, the first picture in the GOP#1 is the first picture of the moving pictures, and the last picture in the GOP#N is the last picture of the moving pictures. A single GOP includes a plurality of (for example, 15) pictures, and playback time of the single GOP corresponds to approximately 0.5 second.
Each picture composing a single GOP is classified into one of an I(Intra-coded)-picture, a P(Predictive-coded)-picture, and a B(Bidirectionally Predictive-coded)-picture. Each GOP includes at least one I-picture. However, hereinafter it is assumed that each GOP includes only one I-picture. Picture types of the plurality of pictures composing the single GOP are arranged in a playback order of, for example, 2B, 3B, 1I, 5B, 6B, 7P, 8B, 9B, 10P, 11B, 12B, 13P, 14B, and 15B, where numerals preceding “I”, “P”, or “B” indicate an order in a data stream. In other words, in the data stream, each picture data is arranged in the order of 1I, 2B, 3B, 4P, 5B, 6B, 7P, 8B, 9B, 10P, 11B, 12B, 13P, 14B, and 15B.
When fast forward playback or fast reverse playback of moving pictures recorded on a DVD is performed using known DVD players, many DVD players are configured to play back only I-pictures among I-pictures, P-pictures, and B-pictures composing moving pictures (see, for example, Patent Document 1).
[Patent Document 1] Japanese Unexamined Patent Application Publication 2001-211405